This invention relates to a safety mechanism for manually portable chain saws. More particularly, the invention relates to safety apparatus for minimizing the possibility of a chain saw operator being injured by a cutting chain.
Manually portable chain saws typically comprise an engine-carrying housing, a cutter bar projecting forwardly from the housing, and an engine-driven cutter chain entrained for endless movement around the cutter bar. The chain saw is designed to be utilized by an operator grasping the machine with both hands. An operator's one hand normally holds a gripping handle mounted on the housing, while the other hand engages a housing control handle for actuating a trigger throttle mechanism.
In some instances of cutting operation, the cutting chain may encounter resistance of a type causing the cutter bar to violently kick upwardly in a manner commonly referred to as "kickback". The abrupt action of kickback may cause an operator's hand to slip from the gripping handle and travel toward the cutting chain, or jerk the cutting chain toward the operator's arm or chest.
It has been estimated that approximately 60% of all chain saw related accidents are either directly or ultimately attributable to this kickback phenomenon.
In still other instances of cutting operation wherein an operator applies downward and forward pressure on the gripping handle, there is a possibility of the operator's hand slipping from the gripping handle and traveling toward the cutting chain.
Experience indicates that if an operator's hand does accidentally engage the rapidly moving cutting chain, the hand can be badly mutilated and/or severed.
Proposals have been heretofore offered which have significantly advanced the state of chain saw safety. These proposals are disclosed in Moore U.S. application Ser. No. 109,574, now U.S. Pat. No. 3,739,475, issued June 19, 1973; Moore U.S. application Ser. No. 294,866, now U.S. Pat. No. 3,793,727, issued Feb. 26, 1974; and Dooley U.S. Pat. application Ser. No. 354,776, now U.S. Pat. No. 3,839,795, issued Oct. 8, 1974, all assigned to the assignee of the present invention. Notwithstanding, however, the significant advancements which these inventions constitute, room for further improvement in the art remains.
Other chain saw safety proposals have been proffered as can be seen, for example, in U.S. Gustafsson Pat. No. 3,776,331, issued Dec. 4, 1973; U.S. Mattsson et al Pat. 3,664,390, issued May 23, 1972; U.S. Irgens Pat. 3,361,165, issued Jan. 2, 1965; U.S. Kiekhaefer Pat. No. 2,610,657, issued Sept. 16, 1952; and British Pat. No. 1,351,546, published May 1, 1974.
Among the proposals heretofore made in relation to chain saw safety mechanisms, many involve braking systems which are not capable of imposing sufficient braking forces to stop the cutter chain soon enough. Moreover, the safety systems may be characterized by numerous mechanical components or relatively complicated arrangements, which are not only more expensive to install and more susceptible to failure, but also occupy too much space on a chain saw housing. It will be appreciated, in this connection, that weight and size requirements of a manually portable chain saw dictate that a safety mechanism be effective, yet involve a minimal number of parts that are capable of compact arrangement.
Many of the previously proposed safety proposals require that the operator continually hold an activating lever in retracted position during chain saw operation to prevent activation of a safety brake. It will be apparent that such an arrangement greatly limits the manipulative freedom of the operator who is restricted to gripping the chain saw in a manner suited for retracting the lever.
In maximizing the effectiveness and convenience of chain saw safety mechanism, it would be desirable to provide a chain saw braking apparatus that is capable of exerting each time a strong, substantially constant braking force, the intensity of which being substantially independent of the manner of actuation. Moreover, such a braking apparatus should be simplistic and compact in design so as to exhibit a minimal chance of malfunction as well as occupy little space on the chain saw housing.
It is, therefore, an object of the invention to alleviate or solve problems of the types discussed above.
It is another object of the invention to provide a chain saw braking mechanism which rapidly and effectively stops a cutter chain in response to the sensing of a dangerous condition.
It is an additional object of the invention to provide such a braking mechanism which is simplistic and compact in design.
It is a further object of the invention to provide such a safety braking mechanism which affords significant manipulative freedom for the operator in supporting and guiding the chain saw.
It is still another object of the invention to provide such a safety braking mechanism which is activated in response to engagement between the hand or arm of an operator and a sensing lever to apply a substantially constant braking force which is independent of the force with which the operator engages the sensing lever.
It is a further object of the invention to provide such a safety braking mechanism which is fast-acting and which can be conveniently recocked.